1. Field of the Invention
The present invention relates to data processing systems and particularly to systems having a system bus connected through a bus converter to an I/O bus, and more particularly to bus-to-bus translation apparatus.
2. Background Art
Many personal computers are provided with an I/O bus for the attachment of I/O adapters. The PC I/O bus, through control signals, may define two address maps, an I/O address map and a storage address map. Transactions over the PC I/O bus are assumed to be targeted for one of the two address maps, and provisions are not made in the PC I/O bus architecture to accommodate any address maps outside the domain of the I/O and storage maps. Direct Memory Access (DMA) transfers initiated by adapters on the PC I/O bus are required to access either the I/O bus attached storage or the system bus attached storage. Thus the I/O bus has effectively a dual storage address map, the basic I/O storage map and the reflected system storage map with no provisions for differentiation between the two maps. For a given address there may exist a machine configuration with an I/O adapter and system storage assigned to the same address within their respective address maps.
A bus converter may be interposed between a system bus and an I/O bus. Since the various I/O devices and the global system storage may have the same address difficulty may be encountered in transferring messages to a particular I/O device. The basic architectural assumptions that all data movement is confined within the address map or maps of the I/O bus makes no provision for accommodating a foreign address map outside the basic architecture.
The present invention solves the above problem by translating an address request to an address which maintains the address of the targeted storage location and in addition contains information identifying the specific I/O device.
The present invention pemits the migration of existing I/O bus architecture and associated adapters to a totally new environment not accounted for in the basic architecture.